1. Field of the Invention
The present invention relates to a laundry drier, and more particularly, to a laundry drier and control method thereof in which a memory of a microcomputer is utilized so that a value comparison can be made between a predetermined reference voltage and a voltage representing a sensed level of moisture (water content or wetness) present in laundry upon completion of a drying procedure, to determine the presence of contamination and compensate for an error in sensing moisture accordingly.
2. Discussion of the Related Art
In general, a laundry drier is an apparatus for drying wet objects, e.g., clothes, after completion of a washing cycle or the like. FIG. 1 illustrates such a laundry drier.
Referring to FIG. 1, a drum 2 for holding laundry is installed rotatably inside a cabinet 1 having a front side in which an entrance 3 is provided. A door 4 is installed in the entrance 3 so that laundry may be placed in the drum 2 via the entrance. A motor 5, installed in an upper space of the cabinet 1, is coupled to the drum 2 via a drum belt 6a such that the drum rotates when the motor is driven. As the drum 2 rotates, the laundry is stirred by a plurality of lifts 7 installed on an inner surface of the drum. Meanwhile, the motor 5 is differentially coupled, via a fan belt 6b, to a fan 9 installed in a space provided behind the drum 2. By thus driving the fan 9, hot air, heated by a heater 11, is circulated through a series of ducts. A circulation duct 8 is provided such that the space provided for the fan 9 communicates with a point near the entrance 3, with an external air supply duct 12 for supplying external air, and with a drain duct 13 for discharging condensed water generated from the circulating hot air.
In the operation of a laundry drier constructed as above, with wet laundry placed in the drum 2, the laundry drier is actuated to drive the motor 5 and thereby rotate the drum, so that the laundry is pulled upward by the lifts 7 to fall back down and be gently mixed. Meanwhile, the driving force of the motor 5 is also transferred to the fan 9, thus circulating the air in the circulation duct 8. The circulating air is heated by the heater 11, and the heated air is supplied to the drum 2 to evaporate the water content of the laundry. Air circulation continues as external air is supplied to the circulation duct 8 through the external air supply duct 12, to be mixed with the heated air in the circulation duct. The water content in the circulating air is condensed to be discharged through the drain duct 13.
The drying of laundry using a laundry drier as described above is typically performed by a controlling apparatus such as that illustrated in FIG. 2.
Referring to FIG. 2, a laundry drier according to a related art is comprised of a moisture sensor 20, installed with respect to the interior of a rotatable drum as described above, for sensing the water content of laundry in the drum to determine the drying status of the laundry and outputting a value indicative of the water content; a voltage converter 30 for converting the water content value to a voltage and outputting a voltage signal; a microcomputer 40 for outputting a control signal to control a drying pattern based on the voltage signal output of the voltage converter; and a load driver 50 for respectively driving a motor 60 and a heater 70 according to the control signal output from the microcomputer.
More specifically, as the drum 2 rotates and the laundry comes into repeated contact with the moisture sensor 20, which is an electrode-type sensor, the water content in the laundry is sensed over the course of a drying procedure. The water content varies according to the drying status of the laundry, and the variation is represented by the voltage output from the voltage converter 30 and input to the microcomputer 40. The microcomputer 40 thus determines the laundry's drying status by reading the input voltage and thereby monitoring the water content as the laundry dries, to control the dry pattern accordingly. In doing so, the microcomputer 40 references the output voltage of the moisture sensor 20 and voltage converter 30 upon initiating a drying procedure and compares the referenced voltage with subsequent outputs over the course of the dry procedure.
After extended use of a laundry dryer as above, however, there is an accumulation of contaminants (e.g., corrosion and a buildup of foreign particles) that inherently forms on and around the electrodes of the moisture sensor 20, which results in a gradual increase of an error present in the sensed values. Moreover, the voltage output from the moisture sensor at the time of initiating a drying procedure differs from that at the completion of the drying procedure, where a contamination of the electrodes has occurred, which inhibits a precise sensing of the output voltage for later stages of the drying procedure. It should be appreciated that such contamination will usually result in an erroneous determination by the microcomputer that the laundry's water content remains after the laundry has been completely dried. In any event, an incorrect sensing of the water content of the laundry may result in an unnecessary continuation of the operation of the heater despite a completion of the drying procedure, to thereby cause overheating or a wasteful power consumption.